Is her surname common for the area you are researching? Could you have conflated two individuals?
If this were my research I might wonder at her being 30 when her illegitimate (first?) child was born, and the 13 year gap between known husband and wife. I would wonder whether she could indeed have been a widow when the illegitimate son was born, and therefore whether I have got the wrong baptism name.
Or could she have left the parish in disgrace in 1825, married somewhere else to someone with the same name, and then been widowed and sent back to the parish she came from? Did her son marry and give a father's name on his certificate? (although he too might lie to maintain respectability).
Is there both a marriage banns record and a marriage service record? Do they both call the lady a widow? I have an ancestor who is called a widower on one, and a bachelor on the other (don't know why). Could be a scribal error, or maybe the clerk had a vague memory that she had already borne a child and took it upon himself to define her as a non-spinster in some way.
Or she could have just lied. A new vicar; a young husband; influential friends; overconfidence... Perhaps she thought she'd chance it.